Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to magnetomechanical electronic article surveillance (EAS) markers, and more particularly to a printed bias used in a magnetomechanical EAS marker.
2. Description of the Related Art
EAS markers are typically attached to articles of merchandise and respond to an electromagnetic field transmitted into an interrogation zone located at the exits of a controlled area. The response of the EAS markers to the electromagnetic field is detected and indicates that the article is being removed from the controlled area without authorization. An alarm can be sounded upon receiving the EAS marker response to alert relevant personnel of an attempt to remove the article.
Conventional magnetomechanical EAS markers that have a magnetostrictive resonator typically use a magnet as a control element either for biasing or deactivation or both. For deactivatable labels, the bias magnet is usually a semi-hard rolled product magnet material. For hard tags that are nondeactivatable, the bias magnet is usually an injection molded ferrite magnet material. The term xe2x80x9cmarkerxe2x80x9d refers to both xe2x80x9ctagsxe2x80x9d and xe2x80x9clabelsxe2x80x9d.
Nondeactivatable EAS hard tags are primarily used in the tagging of soft goods, such as clothing in retail stores. The tags, such as that disclosed in U.S. Pat. No. 5,426,419, consist of a plastic housing that contains a magnetoacoustic resonator element and a clutching mechanism. The hard tag assembly process starts with two halves of the plastic housing that are formed using injection molding. The internal parts (resonator, spacer, bias magnet, and clutch/clamp assembly) are placed within the housing, and the two halves of the housing are sealed together, typically using ultrasound energy. The tag can then be attached to articles to be protected by insertion of the pin body through a portion of the article and into the clutching mechanism. The pin cannot be released to detach the tag from the merchandise unless the clutch is opened by a mechanical or magnetic detacher mechanism designed for the particular tag.
Referring to FIG. 1, a flow chart of the present manufacturing process for hard tags is illustrated. The bias magnets are produced using an extrusion or injection molding process at step 2. Magnetic particles with coercivity higher than 3000 Oe are used to make reusable or nondeactivatable markers. These particles are mixed with plastic binder/resin, and are heated to a molten state. They are then molded into individual pieces with injection molding. The extrusion process can also be used to produce a continuous roll having a strip of magnetic material with a thickness of about 30 to 50 mils. The roll can then be slit and cut into individual pieces with desired dimensions at step 6. Magnetization of the material at step 4 can be performed before or after the cutting process. A batch of resonator strips is also properly cut at step 8 to match with the strength of the magnetic bias strips. The two halves of the plastic housing are formed using injection molding at step 10. The resonator is placed into the cavity formed in the plastic housing halves at step 12. A spacer is placed at step 14 prior to placing the bias magnet at step 16. The clutch assembly is placed into the plastic housing at step 18. The two plastic housing halves are ultrasonically sealed together at step 19 to complete the tag at step 20. Due to the thickness of the magnetic bias, a thin reusable marker is not available.
Referring to FIG. 2, the manufacturing process of deactivatable labels, such as disclosed in U.S. Pat. No. 6,067,015, is similar to hard tags with some significant differences. The bias magnets are not extruded but made of a semi-hard magnetic metal. The housing is made of a vacuum thermal formed polystyrene. There is no clutch assembly used in a deactivatable label, and the spacer and cover are heat sealed to the housing. Referring to FIG. 2, steps that are identical to the steps performed in FIG. 1 are given the same reference numerals. The vacuum-formed housing is produced at 22, after the resonator is cut 8 and placed into the cavity 12, a spacer lid is placed over the resonator and the cavity at 24, and may be heat-sealed in place. The semi-hard bias magnet material is heat treated and annealed to form a roll having desired bias magnetic properties at 26, and after cutting at 6, the bias magnet is placed onto the spacer at 17, and may be adhesively attached. If the bias is not adhesively attached, a cover lidstock material is placed over the bias at 28 and heat sealed to the housing at 30. The bias magnet is magnetized at step 4 to complete the process.
Disclosed in the ""015 patent are bias magnets formed in various shapes to improve the performance of the EAS label. However, all of these deactivatable bias magnets must be cut from a batch of magnetic material, which is normally formed into a roll after the material is properly heat treated and annealed to obtain desired properties. It should be apparent that shapes other than rectangular each present varying degrees of cutting and forming difficulty, which increase the cost to make EAS markers having shaped bias magnets.
There presently exists a need for an EAS tag that is thinner than those made by conventional methods, and for a bias magnet material this is easier to form into various bias shapes such as, but not limited to, those disclosed in the ""015 patent.
The present invention replaces the conventional bias magnets for EAS markers with a paintable or printable bias magnet material, which is either directly painted onto the EAS marker or first placed onto a substrate material, which is then placed into the EAS marker. The material includes a magnetic powder mixed with solvent and resin. This xe2x80x9cbias paintxe2x80x9d is then applied onto the EAS marker. The magnetic powder and solvent provide a very dense layer after drying, which has a magnetic material density that is usually lower than a rolled product, but is higher than that of the injection-molded magnet material.
A first aspect of the invention is a mapetomechanical electronic article surveillance marker having a housing with a cavity formed therein. A magnetostrictive resonator member is disposed within the cavity. A cover is connected to the housing over the cavity capturing the resonator member therein. A bias magnet is disposed adjacent the resonator member, where the bias magnet is a magnetic powder mixed with at least one material to form a paint that is disposed adjacent the resonator by being painted onto the housing or onto the cover. The bias magnet can be painted onto a substrate, and the substrate can be connected to the housing or to the cover wherein the bias magnet is disposed adjacent the resonator. The bias magnet can be formed of a plurality of layers.
A second aspect of the invention is a method of making a magnetomechanical electronic article surveillance marker by the steps of preparing magnetic ink by mixing magnetic particles with a resin and solvent material. Printing the magnetic ink onto a substrate and curing by heating. Providing a housing having a cavity formed therein, cutting and placing at least one resonator into the cavity. Placing the substrate over the cavity wherein the magnetic ink is aligned adjacent the resonator, and connecting the substrate to the housing, capturing the resonator within the cavity wherein the magnetic ink is disposed adjacent the resonator. The method can include printing and curing in a plurality of passes to form multiple layers of magnetic ink on the substrate. The cavity can be formed by printing nonmagnetic ink onto a flat housing material. A cover can be sealed to the housing capturing the resonator within the cavity prior to connecting the substrate to the housing.
A third aspect of the invention is similar to the second except the ink is printed directly onto the housing adjacent the cavity, instead of onto the cover.
A fourth aspect of the invention is a harmonic electronic article surveillance marker having an active element for receiving and radiating an interrogation signal generated by an electronic article surveillance system transmitter. The active element being an elongated strip of magnetic material that produces harmonic perturbations of the interrogation signal, and a plurality of control elements disposed along the active element. The control elements are for being magnetized to deactivate the electronic article surveillance marker. Each of the plurality of control elements includes a magnetic powder mixed with at least one material to form a magnetic paint. The magnetic paint is disposed along the active element by painting in at least one preselected shape.
Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.